Lamotrigine in pregnancy - therapeutic drug monitoring in maternal blood, amniotic fluid, and cord blood.

This study is the first to measure and correlate lamotrigine concentrations in maternal blood, amniotic fluid, and umbilical cord blood and account for distribution of the drug between these three compartments. Concentrations of lamotrigine were measured in six mother-infant pairs at the time of delivery. Daily doses of lamotrigine ranged between 200 and 650 mg. Daily doses were correlated with maternal serum and umbilical cord blood concentrations, and serum levels were correlated with levels in amniotic fluid. Lamotrigine levels in serum correlated strongly with the lamotrigine levels in amniotic fluid (r=+0.986, P<0.001) and cord blood (r=+0.928, P=0.008). The penetration ratio into amniotic fluid was in a range between 0.31 and 0.75 (mean 0.58, SD 0.17); the penetration ratio into the fetal circulation, calculated on the basis of umbilical cord blood levels, was found to be in a range between 0.48 and 1.27 (mean 0.81, SD 0.28). Lamotrigine concentrations in amniotic fluid provided evidence that maternally administered lamotrigine is accessible to the fetus in a manner not previously appreciated. Furthermore, the penetration ratio into umbilical cord blood calculated here is in line with the largest study carried out so far to explore transplacental transfer.